Burns and related wounds present a serious problem in infection control. Noble metal ions such as silver and gold ions are known for their anti-microbial activity and have been used in medical care for many years to prevent and treat infection. Water soluble silver nitrate has been widely used as an astringent and as a potent anti-microbial solution. For example, 10% silver solution preparations are applied directly to ulcers of the mouth; dressings wetted with 0.5% silver nitrate solutions are used to cover second and third degree burns, especially to protect against gram negative infections; and drops of a 1% silver nitrate solution in the eye is still a legally required treatment in many areas of the world for prophylaxis of ophthalmia neonatorum.
The anti-microbial effect of these known silver nitrate solutions appears to be directly related to the concentration of the silver ions. Unfortunately, water soluble silver nitrate solutions provide very little residual activity due to the reactivity of silver ions with chloride, etc. in body fluids. To compensate for this lack of in use longevity, soluble silver solutions, such as silver nitrate, are used at far higher concentrations (3000 to 3500 mg/L) than are required for bacterial control (2 to 5 mg/L) in an effort to extend the duration of the antimicrobial effect. As a result, the solution can have irritating and astringent effects on wounds. For instance 1% solutions used prophylactically for ophthalmia neonatorum must be followed in a few seconds with a 0.85% sodium chloride rinse to prevent conjunctivitis. Burn wound treatment in current use for second degree burns employs 0.5% silver nitrate solutions which must be added frequently throughout the day (usually 12 times daily) in order to replenish the active Ag.sup.+ ion. Also in use are silver sulphadiazine creams, which need frequent reapplication and scraping to remove the debris and chemical barrier, and which may also cause sensitivity or allergic reaction to the sulpha component.
Significant improvements to minimize adverse properties have been sought since the turn of the century. Some efforts have focussed on the use of colloidal solutions of insoluble, poorly ionized salts such as oxide complexes with proteins to reduce the rate of release of silver ions. Other efforts focussed on producing silver in an activated form, for example by depositing it on porous carbon to provide slower release of silver ions, or by activating the silver after deposition, for example by treatment with strong oxidizing agents. Still other efforts were directed at electrical activation of the silver coatings to drive the release of silver, or depositing with an electochemically different, more noble metal so as to use dual metal galvanic action as the driving force to release silver ions. To date, improvements in anti-microbial agents derived from anti-microbial metals such as silver, and wound treatment procedures using same are sought to improve the anti-microbial efficacy of the metal ions, to reduce the frequency of the application of the anti-microbial agent, and to improve infection control in wound treatment. Also needed is a visible indicator of the anti-microbial activity and effect, so as to minimize over application of the anti-microbial agents and unnecessary wound dressing removal, and thus improve patient comfort and minimize sensitivity reactions to anti-microbial metals.
Applicants have developed anti-microbial materials which provide efficacious and sustainable anti-microbial effect. Such materials are described in, for example U.S. Pat. No. 5,454,886, issued Oct. 3, 1995, to Burrell et al. The materials are formed as powders, foils, flakes, coatings or thin films from one or more anti-microbial metals so as to contain atomic disorder.